Multigrid electron tube and method of assembly thereof



June 29, 1965 w. F. GRIFFIN 3,192,428

MULTIGRID ELECTRON TUBE AND METHOD OF ASSEMBLY THEREOF Filed May 25.; 1960 INVENTOR. WILLIAM F GRIFFIN 3 192 428 MULTIGRID ELECTRbN IUBE AND METHOD F ASSEMBLY THEREOF William F. Griffin, Summit, N..l., assignor to Radio Corporation of America, a corporation of Delaware Filed May 25, 1960, Ser. No. 31,600 5 Claims. (Cl. 313-260) My invention relates to electron discharge tubes of the multigrid type and more particularly to an improved and novel mount assembly which facilitates visual alignment of the grid elements.

' In some types of tubes, for example, where a control grid and a screen grid are used, the screen grid lateral Wires are aligned so that they fall in the electron shadow of the control grid lateral wires. By such alignment, the screen grid lateral wires are located out of the direct path of the electron stream, and the number of electrons flowing to the screen grid is minimized. This is important since current flow to the screen grid usually contributes nothing to the output performance of the tube, While excessive screen current may overheat and permanently damage the fragilescreen grid electrode.

To insure proper alignment of the grid lateral wires, it is important that during the assembly of a tube the full length of the control and screen grids be visible and accessible for adjustment until securely fixed in position.

A problem, however, arises as a consequence of the fact that the tube anode electrode must surround most of the aligned portions of the control and screen grids to collect the electrons flowing therethrough, and further is solid, Thus, when the anode electrode is mounted in position on the mount assembly, large portions of the grids are blocked from view, and visual inspection of the grid lateral Wires for alignment is thereby obstructed.

Heretofore, several procedures and means have been devised to allow visual inspection and alignment of the grids either before or after the anode electrode is mounted into position. One method utilizes a flap out in a central region of the anode, which when opened, provides an observation window exposing the grids. Another method relies on an anode which has a smaller axial length than the axial length of the grid lateral Wire array, so that several lateral wire turns can be observed cit-her above or below the end edges of the anode. Another method uses opposed anode half plates so that alignment of the grids can be made after one of the anode half plates has been mounted, but before the opposing plate is welded in position. Still another method uses a single piece anode which is added to the mount assembly after the grids have been aligned, and utilizes .an extra mica spacer to properly locate the anode with respect to the other portions of the mount assembly.

These procedures have the disadvantages of limiting the numbers of turns of the grid lateral wire available for observation during the alignment operation, of not providing for sufficient grid coverage by the anode, of requiring additional steps in the application of the anode,

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having element-receiving apertures into which mounting ears or endportions of the tube electrodes are inserted. The mica spacers provide support for the electrodes, and the location of the different apertures with respect to one another determines the spacings between the tube elec: trodes.

Also, since many of these tubes have high electrical voltages applied to their anodes, the anodes of these tubes I are usually so designed that the active or electron collector requiring extra tube elements to complete the mount assembly.

Accordingly, it is an object of this invention to provide a novel electron tube structure whereby the parts of the tube may be more accurately and expeditiously examined and adjusted. I

More particularly, it is an object of this invention to provide an improved method of assembly and construction of a multigrid tube which facilitates grid alignment.

A further object is to provide a novel means tor supporting and locating an anode electrode with respect to the other tube electrodes in an electrode cage.

As is well known, electron discharge tubes of the type described usually comprise at least two mica spacer plates ing portions thereof may be spaced in close relationship to the other electrodes, while the anode mounting ears may be spaced at large distances therefrom. The purpose of the large distance spacings is to prevent voltage breakdown or electrical current leakage across the mica spacers between the anode mounting ears-and the other electrode end portions in engagement with the mica spacers. Furthermore, to reduce the number of possible leakage and breakdown paths on the mica spacers, the fewest number of anode mounting ears as possible are used.

It is noted, however, that the restriction on the number of mounting cars used, and the distance of these cars from the active portions of the anode, often create a condition wherein the anode is insecurely fixed or supported in relation tothe other mount assembly electrodes, Such insecure mounting permits excessive vibrational movement of the anode with respect to the other electrodes when the tube is subjected to external mechanical shocks. This movement, as well known, produces undesirable microp'honic noise in the output signal of the tube.

' Therefore, a further object of this invention is to pro vide improved means for restricting the vibrational movement of the tube electrodes under operating conditions.

Another object is to provide a novel means which utilizes anode mounting ears for supporting and locating an anode electrode with respect to other tube electrodes of an electrode cage, and wherein the current leakage between said mounting ears and said other electrodes is minimized.

Furthermore, in certain types of electron tubes, as will be more fully described hereinafter, it is desirable to provide inwardly extendingwfins or projections on the anode electrodes. These fins cooperate with the active portions of the anodes and serve to improve the electrical performance of the electron tubes. As will be seen, however, incorporation of such fins in the prior art tubes usually necessitates the use of extra par-ts and mounting operations which increase the cost of the electron tube.

A still turther object of this invention, therefore, is to provide an anode having as an integral portion thereof an inwardly extending fin of the type described.

One form of electron tube in which the present invention is useful comprises a tube having electrodes including a cathode, a pair of aligned grids, a beam confining plate, and an anode. The grids are wound with the same number of lateral wire turns per inch so that each lateral wire turn of the inner grid shades the corresponding lateral wire turn of the outer grid from the cathode.

In the assembly of this type electron tube in accordance with my invention, a first mount assembly comprising a cathode and at least two grids is assembled between two mica spacer plates. This mount assembly permits full observation of the grid turns since the anode is not yet added to the mounts and the grids may be readily aligned and anchored as described below. After the grids have been aligned, the anode is added to complete the of the half plates in contact and secured to one another. Mounting ears at the top and bottom ends of the plate halves engage portions on the periphery of the mica spacers, and the plate flanges are welded together to form a box-like anode structure wrapped around the mount assembly. The plate mounting ears and the mica edge portions they engage are soshaped as to permit unique registry of the one with the other whereby the plate halves are properly located with respect to the other mount assembly electrodes. In addition, the area of the mica spacers is slightly larger than the cross-sectional area enclosed by the plate halves, which requires that the plate halves must be tightly squeeze'dtogether against the mica spacer edges to permit joinder and welding of the' plate flanges. and supported by the mica spacers.

In essence, the anode isrigidly locked to This construction has the additional advantage of reducing tube noises due to vibration of the mount electrodes, as will be more fully described hereinafter.

lowing description taken in connection with the accompanying drawings, wherein:

FIG. 1 is an exploded view in perspective with parts broken away to, show details of construction of an electron tube made according to this invention;

- FIG. 2 is a plan view with parts broken away of the mount assembly shown in FIG. 1 and mounted within an evacuated envelope;

FIG. 3r-is an enlarged detail view in section of a portion of the anode and mica structure shown in FIG. 1; and

FIG. 4 is a fragmentary view of a portion of the structure shown in FIG. 1 for illustrating proper grid alignment.

Referring first to FIG. 4, control grid support rods and screengrid support rods 11, portions of which are shown, hold the control grid wires 12 and screen grid wires 13, respectively, positioned by grooves 14 suitably spaced on the support rods 10 and 11. The positions of the control grid and screen grid lateral wires in PEG. 4 are shown in proper alignment. In this case, it is noted that the control grid lateral wires 12 and screen grid lateral wires 13 present a distinctive pattern wherein corresponding turns appear to coincide over the entire surface portion of the cathode 17, as viewed along a line perpendicular to the surface of the cathode. Because of the distinctiveness of this pattern, the. alignment of these grid lateral wires may be readily checked. Alignment may usually be secured by longitudinally moving the control grid support rods 1t and screen grid support rods 11 in the proper direction, up or down, with respect to each other. Since the grooves 14 are evenly spaced and firmly hold the grid wires, such corrective movements may align all of the grid wires simultaneously. Such adjustment is most readily accomplished when the fulllength of the grid winding is visible, since it permits direct checking of all the turns rather than only a representative few. That is, during manufacture and subsequent handling before assembly, it often happens that individual turns of the screen grid lateral wires 13 or the control grid lateral Wires 12, become bent or pushed out of position. As a 7 result, these displaced wires are not properly aligned even. after the support rods 1t? and 11 are properly positioncd. Allof'these misaligned portions may be discovered by visual inspection only if all of the grid turns are visible, as in practicing the present invention, and may plate already mounted thereon. FIG. 1 will be referred to in connection with the construction of the mount assembly. V

The cathode 17 is first threaded through a central aperture of bottom mica spacer 18. The control and screen grids are then dropped over the cathode 17 and the support rods 10 and 11 of these grids are threaded through corresponding apertures of the mica spacer 13. A beam confining plate 20 is. subsequently positioned by threading its mounting cars 21 to the. corresponding apertures in the spacer 18 also. The aligningmica spacer 22 is then slipped over the electrodes by orienting and associatingcorresponding apertures in the aligning mica spacer 22 with respect to the cathode 17, support rods, 10 and 11, "and the beam platetabszl. Several of the beam plate mounting ears 21 are then bent over .onto .the top and bottom mica spacers to lock these spacers and the electrodes together. The support rods wand 11 and other beam plate tabs are welded at their bottom ends to the leads 25 protruding from the stem Ziato complete the mount assembly;

The, purpose of the beamplate is to allow electronsto pass to the plate through the control andscreen grids, but to prevent passage of secondary emitted electrons from the plate to the support rods of the screen grid. Thus,

the beamplate is provided with a large windowin the path of the electron stream, and visualinspection of the aligned portions of the grids is notobscured by this electrode. Y a

Prior to welding, the leads 25 to the supporting rods l0 and 11, the grids; are moved with respect to one another as previously described to align the winding turns 12 and 13. After welding, a careful final movement and alignment of the, grids may be accomplished by a slight bending of the leads 25 welded to the grid support rods. T he frictional contact between the mica spacers 18 and 22 and the grid support rods it) and-l1 along with the fixing of the grid support rods to the rigid stem leads 25, is sufficient to prevent relative movement of the'control. andscreen grids'and to preserve the alignment of these grids during subsequent; assembly operations and use of the finished tube.

With reference to FIG. 1 there is shown an anode half plate 31 detached from the mount .assembly.- Such half plate consists of two large. channel-shaped sections 32 connected by a flange 33 and having flange 34 extending laterally from its sides. Half plate 36, shown in FIG. 1 in assembled relation,with respect to spacers 1'8 and 22, is identical to half plate 31, and when the latter half plate is added to the mount assembly, the plates, are Welded together at their coincidentv laterally extending flanges. f

To locate each of the half plates withrespect to one another and to the other electrodes when they, are added to the mount-assembly, eachplate half is provided with plate mounting ears iti, extending from each end of sections 32.. The purposeof these extending ears is to frictionallyand tightly engagepredetermined edge portions of the mica spacers. As shown in FIGS. 1 and 2, the plate cars are composed of two parallel flanges 41, connected by .a third flange 42. Steps 43 are cut into the edges of flanges 41 and define two regions 46 and 47 of the plate ears (FIG..3). The purpose of the steps 43 is to provide shoulders to properly locate the plate halves in axial relation with respect to the mount assembly, and to dispose the remainder of the plate body from contact with the mica spacers to reduce leakage current along the mica spacers betweenthe anode and other tube electrodes.

Included in the connecting flanges 42 and positioned.

between steps 43 and the adjacent ends of theears 40, are dimples 45, as shown in FIGSJI, 2 and 3. These dimples, as will be seen, not in cooperation with steps 43 and fiangesl tov firmly lock the. mica spacers to the plate ears. a e

As shown in FIGS. 1 and 2, the mica spacers 18 and 22 have a plurality of outwardly extending projections 48 spaced around the periphery of the mica. These projections, as is well known in the art, serve to flexibly support and center the completed mount assembly in the glass closure envelope 51.

In accordance with this invention, four additional extensions 49, or flats as they will be referred to, are provided in the edges of the mica spacers. These flats are of rectangular shape and are substantially of the same size and shape as the area included between the portions of the flange 41 defining region 46. Also, flats 49 are very carefully located with respect to the other elementreceiving apertures in the mica spacers, and as will be described, serve to properly space the anode with respect to the other tube electrodes.

The addition of the plate halves to the mount assembly involves operations which comprise locating each plate half between the two mica spacers, causing the plate ears 40 to engage the spacer flats 49, and welding the plate halves together at their extending flanges 34.

As shown in FIGS. 1, 2 and 3, regions 46 of the plate ears register with the edges of the spacer flats 49, while steps 43 of flanges 41 extend inwardly of the mica spacers for positively fixing the axial location of the plate halves.

Location of the half plates with respect to one another and to the other mount assembly electrodes is determined, as mentioned, solely by the mica flats. In the practice of this invention, spacing 11 (shown in FIG. 2) between edges of opposing flats of the mica spacers is made just slightly larger than twice the spacing a between the inside of the plate ears and the outside surface of the plate flanges. In this embodiment, the difference is 0.010 of an inch for a mica flat spacing b of 0.440 of an inch. As a result of this dimensional difference, it is necessary to tightly squeeze the two half plates against the edges of the mica spacers and to deform the extending flanges 34 into engagement for Welding. The spacing difference is shown exaggerated in FIG. 2 wherein the half plates are shown (dotted) before and (solid lines) after welding.

The squeezing of the half plates, it will be noted, causes a deformation of flanges 34 only, while the shape of the remaining portions of the half plates is unaffected.

Flanges 34 are sufficiently resilient that once welded, they serve as tensioned springs to keep the plate ears 40 tightly clamped to the edges of the mica flats 49. In the practice of this invention, no special jigs or flange deforming means need be employed, since the pressure supplied by the electrodes used to weld the half plates is sutficient to bring the flanges 34 together.

An important feature of this invention is the fact that the squeezing together of the plate halves against the mica edges causes some slight flexing of the mica. The extent of this flexing is so small as not to affect the anode spacing, but enough to slightly reduce the cross-sectional area of the mica spacer element-receiving apertures and to increase the frictional contact between the mica spacers and the ends of the tube electrodes. The effect of this is to reduce rattle of the tube electrodes within the mica apertures caused by vibrational movement of the electron tube, and hence to reduce microphonic tube noise.

To prevent excessive flexure displacement of the thin mica spacers 18 and 22 with respect to the anode ears, dimples 45 are provided. When the half plates 31 and 36 are first added to the mount assembly, the plate ears 40 are fitted to the mica flats 49 with the mica flat edges 53 located between steps 43 and dimples 45, as shown in FIG. 3. As the plate halves are squeezed against the mica edges 53 to join flanges 34 for welding, the dimples 45 serve as a stop to prevent upward flexure of the mica edges away from the plate ear steps 43. After welding, the mica edges are thus firmly locked within the plate ears.

Furthermore, engagement between the plate ears and the mica spacer flats, as herein disclosed, is a more positive means of fixing an anode to mica spacers than the usual method of inserting plate ears through apertures therein. In the latter method, the object is to have the plate ears bite into the mica walls to be locked thereto. Frequently, however, oversize plate ears bite too deeply into the mica and fracture or delaminate the aperture walls and thus destroy the friction fit of the plate ears to the mica. Conversely, undersize plate ears may fit too loosely within the apertures and allow rattle of the ears. In either case, the excessive play of the ears within the mica apertures contributes towards the production of microphonic noise. The locking of the plate ears to the mica spacers in accordance with my invention is done without any such biting of the ears into the mica.

A further advantage of my invention over the prior art is the extra large spacings obtainable between the plate ears and end elements of the other tube electrodes. Because of the fragile nature of micas, large land areas of unbroken mica must surround all element-receiving apertures in the mica to give strength to the aperture walls. Consequently, the maximum distance between the plate ears .and the other electrodes disposed within the anode in the prior art tubes is determined by the size of the mica bridge that must be provided between the mica spacer outer edges and the anode-receiving apertures in the micas. In accordance with my invention, however, no outer mica bridge is required since the plate ears engage peripheral portions of the mica spacers. As a result, the voltage breakdown and leakage cur-rent characteristics of tubes made according to my invention are significantly superior to that of tubes made in the conventional manner.

A still further feature of my invention is the ease with which snivet fins may be added to my anode electrodes. The use of these fins is well known in the art, and they are often included in electron tubes of the grid-aligned, power output type for improving the electrical performance of the tubes. As shown in FIG. 1, a snivet fin 50 may comprise a single emboss or projection which is desirably positioned midway between the side edges of flange 33 and which extends inwardly therefrom and toward the center of the electron stream.

As mentioned, the use of snivet fins in the prior art tubes usually involves the addition of extra parts to the anode electrode. The reason for this is related to the fact that most tubes using such fins are power output tubes which also require the inclusion of outwardly extending heat dissipating flanges on the active portions of the anode. The purpose of these flanges is to dissipate heat produced at the anode by the kinetic energy of the heat electrons striking the anode.

Moreover, the practice in the prior art is to position these flanges on the anodes adjacent to the desired anode location of the snivet fins. Such flange positioning is determined by the requirements of anode construction, mounting and effective heat removal. The reasons for these requirements are well known, however, and further discussion of them will be omitted for the sake of brevity. Also, due to the mechanics of conventional fabricating means, it is not possible to form anodes having both inwardly and outwardly extending flanges which are positioned closely together on the anode. Thus, in such tubes, the anodes are generally formed with integral heat dissipating flanges, while the snivet fins are added to the anodes in a separate mounting operation.

In accordance with my invention, however, flanges 37 at the side edges of flange 33 serve to dissipate the heat produced at flange 33, and, as shown in FIG. 1, are spaced :at some distance from snivet fin 50. The advantage to this construction is that the separation of the flanges from the snivet fin permits the fabrication of my anode with both these elements included as integral portions thereof. This, of course, avoids the necessity of adding the snivet fin in an extra operation and results in a significant cost savings.

What is claimed is:

1. A multigrid electron tube having a cathode electrode and a plurality of coaxial grid electrodes surrounding said cathode, said grids having aligned lateral wires, a pair of oppositely disposed insulating electrode spacers at opposite ends of said cathode and grid electrodes spacing and securing said electrode-s together, and a multi-part anode surrounding said electrodes and engaging the peripheries of said spacers and supported thereby, said multi-part anode comprising two oppositely disposed half plates, each of saidhalf plates formed to include at least two channelshaped sections joined by a connecting flange, said connecting flange-having a fin projecting therefrom, each of said sections having a flange extending laterally from a side of said sections, and said half plates disposed around said electrodes with the flanges of one of said half plates in apposition to the flanges of the other of said half plates, said half plates being fastened together at said flanges, and said fin extending inwardly of said half plates towards said grid electrodes.

2. A multi-grid electron tube comprising a stern having a plurality of leads extending therethrough, a plurality of electrodes mounted on said stem, and a pair of insulate ling spacers having electrode receiving apertures therein,

saidelectrodes including a cathode,a pair of grids having aligned lateral wires, and a beam plate having mounting tabs at its upper and lower ends, the ends of said electrodes being received within said spacer apertures for spacing said electrodes with respect to each other, said pair of spacers being mounted on said mounting tabs and being maintained in parallel spaced apart relation'thereby, and each of said gridelectrodes being rigidly secured to a corresponding one of said stem leads for fixing the relat-iveaxial positioning of said grid electrodes, said aforementioned stem, electrodes, and spacers providingwhen assembled, a rigid and self-supporting assembly, an anode surrounding said electrodes, said anode comprising two flanged sections formed of resilient material and having mounting ears thereon, said sections being disposed about said electrodes with the flanges of one of said sections in apposition to the flanges of the other of said sections With said mounting ears embracing peripheral portions of said spacer-s and being supported thereby, said sections being resiliently'deformed and fastened together at said flanges, wherebysaid flanges serve as tensioned springs to preserve said mounting ears in tightly embraced relation about said peripheral portions.

3. A multi-grid electron tube comprising a stem having a. plurality of leads extending therethrough, a plusee spcct to each other, said pair of spacers being rigidly mounted on said mounting tabs and being maintained in parallel spaced apart relation thereby, and each of said grid. electrodes being rigidly secured to a corresponding one of said stem leads for fixing the relative axial positioning of said grid electrodes,.said aforementioned stem, electrodes, and spacers providing, when assembled, a rigid self-supporting assembly, and a multi part anode surrounding said electrodes, said, anode engaging peripheral portions of said spacers and being supported thereby.

4. A multi-grid electron tube comprising :a rigid and self-supporting mount assembly including a stem having a plurality of leads extending therethrough, a plurality of electrodes mounted on said stem, and a pair of electrodespacers, said electrodes'including a cathode and a pair of coaxial grids having aligned lateral :wires, said spacers being disposed at opposite ends of said electrodes for spacing and-securing said electrodes with respect to each other, means for maintaining said spacers in spaced and parallel relation :to one another, and each of said grid electrodes being rigidly secured to a corresponding one of said stem leads for fixing the relative axial positioning of said grid electrodes, and a multi-part anode mounted on said mountassembly, said anode being disposedabout said electrodes and engaging the peripheries of said spacers and being supported thereby, whereby visual inspection and alignment of the lateral wires of said grids may be obtained after said electrodes are mounted on said stem. and prior to assemblyof said anode to said spacers. V

5. An electron tube including a rigid and self-supporting mount assembly comprising a plurality of electrodes,

a pair of parallel oppositely disposed spacers mounted on the ends'of said electrodes, means for maintaining said spacers in spaced apart parallel relation, and means for fixing the axial positioning-of said electrodes with respect to one another, and a multi-part anode engaging the peripheries of said spacers and being supported on said mount assembly thereby, wherebyvisual inspection and alignment ofsaid electrodes may be obtained prior to assembly of said anode to said spacers.

References Cited by the Exaniiner V UIJITED STATES PATENTS Vodden 3 l3261 DAVID J. GALVIN, Primary Examiner.

RALPH G. NILSON; BENNETT G. MILLER,

Examiners. 

5. AN ELECTRON TUBE INCLUDING A RIGID AND SELF-SUPPORTING MOUNT ASSEMBLY COMPRISING A PLURALITY OF ELECTRODES, A PAIR OF PARALLEL OPPOSITELY DISPOSED SPACERS MOUNTED ON THE ENDS OF SAID ELECTRODES, MEANS FOR MAINTAINING SAID SPACERS IN SPACED APART PARALLEL RELATION, AND MEANS FOR FIXING THE AXIAL POSITIONING OF SAID ELECTRODES WITH RESPECT TO ONE ANOTHER, AND A MULTI-PART ANODE ENGAGING THE PERIPHERIES OF SAID SPACERS AND BEING SUPPORTED ON SAID MOUNT ASSEMBLY THEREBY, WHEREBY VISUAL INSPECTION AND ALIGNMENT OF SAID ELECTRODES MAY BE OBTAINED PRIOR TO ASSEMBLY OF SAID ANODE TO SAID SPACERS. 